1. Field of the Invention
The invention relates to a process and apparatus for chlorinating flowing water supplies to control the growth and reproduction of microorganisms present in these waters.
2. Description of the Prior Art
Micro irrigation systems, as illustrated by drip irrigation systems, and other flowing water supplies, e.g. refinery, steel mill and other industrial wastes are very susceptible to problems created by microbiological organisms present in water. In the case of drip irrigation systems, which are described on page 30 of the Western Fertilizer Handbook, which definition is incorporated herein by reference; the organisms are commonly algae of various types, and bacteria which use iron, manganese, and/or sulfur for their metabolism. However, depending on the water source, any microbiological organism that grows in large colonies can create problems for the micro irrigation systems. Typically these problems include interference with the proper operation of the system such as plugging of the filters resulting in excessive back flushing of the filters, high pressures at the filters, plugging of emitters, poor distribution of water and other chemicals throughout the irrigation system, segregated areas with extremely high or low pressures and the need for frequent hose and flushing which is very labor intensive and costly.
Currently used for microorganism control is chlorine gas or bleach, a dilute solution of sodium hypochlorite. In the case of chlorine gas, many areas have banned the use of the gas due to the hazards of handling it. Although it is economical, the handling problems and special training of the personnel have dramatically, if not totally, eliminated its use.
Bleach is much easier to handle but due to its low concentration of available chlorine (maximum 12% available C12) large volumes of solution must be used which present other handling and safety issues.
In either case, the handling, safety and liability issues with these materials resulted in their limited and occasional use in micro irrigation systems as a "shock treatment" (15-20 ppm C12) or "superchlorination" (between 25-1000 ppm C12). Bleach has never been fed continuously and gaseous chlorine only rarely fed continuously. In both cases, these chlorine sources are fed as a "one time" treatment to a reservoir or directly into the irrigation system.
Calcium hypochlorite is a chlorine source that eliminates the handling problems that are present with chlorine gas and bleach. Calcium hypochlorite contains 67 percent available chlorine and is a solid. As a result, high concentrations of available chlorine are achievable and the solid can be handled and transported very easily. Calcium hypochlorite solid has been used routinely as a chlorine source in the treatment of swimming pools and related systems when a chlorine source is required for biological control. These systems are, however, at ambient pressures. To feed any chlorine-based product into a micro irrigation system, a pressurized system is required. In the case of gaseous chlorine, feeding into a pressurized system is easy due to the high partial pressure of chlorine gas. In the case of bleach, a solution of bleach can be fed into the irrigation system using high pressure pumps, but there are three main problems with the bleach approach.
First as mentioned earlier, large storage tanks or many drums would have to be used which presents handling problems.
Secondly, a chlorine source such as bleach will "vapor lock" the high pressure delivery pump. This happens because the hypochlorite anion, in solution, is in equilibrium with chlorine gas. Tiny bubbles form gas pockets which stop the pump from delivering the bleach solution into the system. When this happens, the pump has to be continuously re-primed making this approach extremely difficult, if not impossible.
Thirdly, the high pressure pumps and related equipment must be made of stainless steel or other suitable material due to the corrosive nature of the bleach. This makes such systems too expensive for many applications.